Small appliances such as the Ninja are usually carefully engineered not to draw more than 1800 watts which is 15 amps at 120 VAC (Amps = Power / Voltage). Always check the power requirements of any appliance, which is usually always listed by the manufacturer.
So, if your kitchen circuit breaker can handle at least 15 Amps (which is usually the case) you should be ok provided you aren't simultaneously using any other power on the same circuit. I regularly use an 1800 Watt
Ninja SP101 Digital Air Fry Countertop Oven in my TT and have no issues, but it is pushing things a bit on a 15 amp breaker. If you have a 20 Amp breaker, all the better.
It would be wise to try to keep the power requirements of small appliances used in RVs to no more than 1500 Watts. This would give more leeway and help ensure no issues.
If you buy a power-hungry small appliance and it blows the breaker, you'll know immediately that you can't use it. If it doesn't, then as long as you don't need to use any other significant power on that circuit, you should be fine.